1. Field of the Invention
The invention relates generally to control signal generators and, more particularly, but not by way of limitation, it relates to a digital signal generator for use in controlling a seismic vibrator.
2. Description of the Prior Art
The prior art includes various forms of analog signal generator which have been utilized in controlling frequency, duration and amplitude of seismic vibrators. In general, the prior equipment has taken the form of analog generation devices for generating the prescribed replica or control signal. Such prior types of generator have not been capable of providing the frequencies necessary to resolve thin layering in geologic events, nor have they been able to provide the requisite sweep linearity to minimize ghosting or correlation background. One known prior teaching that is directed to digital construction of a prescribed control signal is the subject of U.S. Pat. No. 3,460,648 in the name of Waters et al. This patent describes a digital system for providing accurate sweep signals, but it has proven impractical due to the very large drum requirements when utilizing such computational digital equipment.